Various single layer and multiple layer cling films have been used for wrapping steel coils and other articles. Cling films are typically based on polyethylene homopolymers or copolymers including, without limitation, low density polyethylene, linear low density polyethylene, ethylene vinyl acetate and the like. In addition to the polymer components, these films typically include a balance of additives which are intended to improve cling, and additives employed for other purposes which may have an undesirable anti-cling effect.
A cling film must have the ability to stick or cling to itself, or to other films having the same composition. One conventional cling film is based on linear low density polyethylene modified with a cling additive, such as polyisobutylene, a volatile corrosion inhibitor, such as sodium nitrite, as well as other chemicals described below that bloom to the surface and deposit on the steel surface to inhibit corrosion. The corrosion inhibiting chemicals tend to diminish or eliminate the cling of the linear low density polyethylene film. The polyisobutylene restores the cling to the film, so that the film will cling or stick to itself during wrapping of an article.
Multiple layer films have also been developed, having very high cling properties in an outer facing layer of the film and corrosion inhibiting additives in an inner facing layer. The corrosion inhibiting additives can thus readily migrate to the article being wrapped. The very high cling properties of the outer facing layer tend to offset the low cling properties of the inner facing layer, so that the two surfaces adequately cling together during wrapping.
Other cling films include volatile corrosion inhibitors applied as a coating in stripes or other spaced apart patterns. The areas on the film away from the stripes are devoid of these additives, allowing opposing film surfaces to cling together during wrapping. These cling films are relatively complex and expensive to manufacture.
Another difficulty encountered with prior cling films (both single layer and multi-layer) is that they may puncture and tear when exposed to the sharp edges of steel coils or other articles being wrapped. Thus, there is a need or desire for a cling film system which a) provides improved cling properties while aiding corrosion resistance, b) is relatively inexpensive to manufacture, and c) has improved toughness and puncture resistance.